This invention relates to a new composition of matter, the production of a zeolite adsorbent and a separation process employing same. More specifically, this invention concerns the production of a zeolite adsorbent, which preferentially adsorbs ethylbenzene from ortho-, meta- and paraxylene C.sub.8 aromatic mixtures. The invention, therefore, also relates to a hydrocarbon separation process employing the specifically prepared sieves to effectively separate ethylbenzene from C.sub.8 aromatic isomer mixtures of ortho-, meta-, and paraxylene.
It is well known in the separation art that certain molecular sieve adsorbents can be employed to separate paraxylene from C.sub.8 aromatic isomer mixtures, containing ethylbenzene. The adsorbents generally employed are those as found adequately described in several patented inventions in which paraxylene is separated and recovered from C.sub.8 aromatic isomer streams. It is also known and adequately described in U.S. Pat. No. 3,761,533 and U.S. Pat. No. 3,201,491 that in adsorption separation processes of liquid feed mixtures a technique of employing a moving bed type adsorption process wherein said moving bed comprises adsorbent particles which are countercurrently contacted with streams of liquid feedstock and desorbent, results in a high degree of purity for the adsorbed component recovered as product. This process and the so-called "simulated countercurrent flow system" wherein the solid desorbent particles are stationary have been proposed and disclosed in the above-referred to patents.
Other processes, such as commercial elution chromatography, have also been proposed for the separation of components from fluid mixtures. In these processes, the selective retardation of one or more of the components of the fluid mixture as the fluid uniformly moves through a column containing a stationary adsorbent; the retarding resulting from the distribution of the components of the mixture between the adsorbent and the bulk fluid as the fluid moves past the stationary phase. The latter process is commonly called "elution chromatography" and the separation of C.sub.8 aromatic isomers will be operated in such a way as to pass the feed stream over an adsorbent, i.e., molecular sieve that preferentially adsorbs the paraxylene at a rate slow enough for essentially all the paraxylene to be adsorbed rather than breaking into the raffinate stream. The sieve bed could then be washed with a desorbent to desorb nonpara materials, and finally pure para could be desorbed from the sieve bed with a liquid material, i.e., desorbent, which can thereafter be easily separated from the para by distillation.
The prior art in general has not recognized the effects of rubidium ions co-exchanged with sodium ions of Type X zeolites. It has been found that the rubidium exchanged Type X zeolites generally cause the selective retention of ethylbenzene from the C.sub.8 aromatic isomer mixture rather than the selective retention of paraxylene; hence, the use of said sieves provide a means whereby ethylbenzene may be efficiently separated and recovered from said feedstream.